Various techniques have been proposed to display the remaining amount of a compressed gas stored in a tank (see, for example, JP-A-2005-240854). The technique disclosed in this cited reference JP-A-2005-240854 displays the remaining amount of a compressed gas fuel (compressed gas) stored in a tank, based on the pressure and the mass of the compressed gas fuel. Other known relevant techniques include those disclosed in JP-A-2006-226511 and JP-A-2005-283127.
From the safety standpoint, there are standards set for a tank used for storage of a compressed gas with regard to the pressure and the temperature of the stored compressed gas. The compressed gas is filled into the tank according to these standards. Namely the amount (mass) of the compressed gas filled into the tank is limited by the pressure or the temperature of the compressed gas in the tank. For example, on the condition that the temperature of the compressed gas in the tank is increased by adiabatic compression in the course of filling the compressed gas into the tank and reaches a preset reference temperature, the filling of the compressed gas into the tank is stopped even when the pressure of the compressed gas in the tank is lower than a preset reference pressure. On the condition that the temperature of the compressed gas in the tank increases by adiabatic compression is still lower than the preset reference temperature, on the other hand, the filling of the compressed gas into the tank is stopped when the pressure of the compressed gas in the tank reaches the preset reference pressure.
The technique disclosed in the cited reference JP-A-2005-240854, however, does not make display of a symbol ‘FULL’ representing that the amount of the compressed gas filled into the tank reaches its full level, when the amount (mass) of the compressed gas filled into the tank is limited by the temperature of the compressed gas in the tank. Even once the pressure of the compressed gas in the tank reaches the preset reference pressure to make display of the symbol ‘FULL’, a decrease in pressure of the compressed gas in the tank over time with a decrease in temperature of the compressed gas leads to the disappearance of the display of the symbol ‘FULL’ without any consumption of the compressed gas. The absence of the display of the symbol ‘FULL’ in spite of the compressed gas filled into the tank to its full level makes the user feel strange.